1. Field of the Invention
The present invention relates to a signal recording-reproducing apparatus for recording and/or reproducing the signal on and/or from a moving recording medium, and in particular to a signal recording-reproducing apparatus which is equipped with a supporting plate for elastically supporting a read/write element such as a magnetic head and the like relative to a recording medium.
2. Description of the Prior Art
It is well known that flexible disk drivers (FDD's) are used as external data storage for computers and the like for magnetically reading information from and/or writing information on a flexible magnetic disk. Recently such FDDs are progressing rapidly in miniaturization and high capacity so that they are required to have high recording density. In this respect, it is well known that increasing recording frequency and narrowing the magnetic gap of a magnetic head is useful to attain high recording density.
However, when the magnetic gap is narrowed in width, for example, the variations in spacing between a disk and the magnetic head due to warping of the magnetic disk or the like have a bad influence on the output characteristics of the magnetic head.
Therefore, it is required to maintain the above mentioned spacing as small as possible by stabilizing the contact between the magnetic head and the magnetic disk. In order to satisfy the above-mentioned requirement, referring to FIG. 1, a head supporting plate 1 is generally used for conventional FDD's. The head supporting plate 1 is made of a flexible and elastic material and includes first, second and third concentric supporting frames 1a, 1b and 1c which are arranged concentrically from the center of the supporting plate 1 to the outside. A magnetic head 2 is mounted on the first supporting frame 1a and the third support frame 1c is mounted on a head arm (not shown). Thus, the magnetic head 2 is installed in the head arm (not shown) through the head supporting plate 1.
The supporting frames 1a, 1b and 1c are interconnected through first and second tie bars 1e and 1d in such a way that the first and second supporting frames 1a and 1b are swingable relative to the third supporting frame 1c. More specifically, as shown in FIG. 1, the first tie bars 1e interconnect the first and second supporting frames 1a and 1b in the direction (indicted by the arrow X) perpendicular to the direction of relative motion between the magnetic head 2 and a disk (not shown), so that the first supporting frame 1a can swing in the directions indicated by A and B in FIG. 1 relative to the third supporting frame 1c by the elastic deformations (torsional displacements) of the first tie bars 1e and also can move freely in the vertical direction indicated by the arrow Z. In like manner, as shown in FIG. 1, the second tie bars 1d interconnect the second and third supporting frames 1b and 1c in the direction (indicated by the arrow Y) of relative motion between the magnetic head 2 and the disk. Therefore, owing to the elastic deformations of the second tie bars 1d, the first supporting frame 1a can swing in both directions indicated by C and D as shown in FIG. 1 relative to the third supporting frame 1c through the second supporting frame 1b and furthermore can move freely in the vertical direction indicated by the arrow Z.
As described above, in the prior art, so far the magnetic head arm 2 is installed in such a way that it can swing relative to the head arm, whereby the magnetic head 2 can follow the surface of the disk. A pair of magnetic heads 2 supported by the head supporting plates 1 in the manner described above are each disposed on both faces of the disk, so that the disk is sandwiched and held by the magnetic heads 2. In the case of such construction described above, the head supporting plate 1 is energized by one or more springs (not shown) so as to press against the disk.
However, when the disk is rotated with the magnetic heads 2 being supported by the head supporting plates 1, respectively, as shown in FIG. 2, the rotation moments MA and MB in the directions A and B (see FIG. 1) are produced on the side at which the disk 3 leaves the magnetic heads 2 such that the head 2 is caused to lift from the surface of disk 3 owing to the rotation of a disk 3 in one direction (indicated by the arrow R) and contact pressure force of the springs. Furthermore, in the case of the head supporting plate 1 of the conventional type described above, the second tie bars 1d can swing freely in both directions A and B (See FIG. 1) so that when the rotation moments MA and MB in the directions A and B are produced, as best shown in FIG. 2, one side end of each magnetic head 2 very frequently tends to lift and consequently moved away from the surface of the disk 3. As a result, there has been the problem that a loss of spacing occurs. In order to solve such a problem, it has been proposed to increase the pressure forces of the springs, but this causes the frictional force produced between the magnetic heads 2 and the disk 3 to be increased, resulting in a decrease of durability of the magnetic disk or the like.
Furthermore, the upper head supporting plate 1 is forcibly pressed against the surface of the disk 3 by the spring so that the lower head supporting plate 1 is forced to be flexed as shown in FIG. 3B. When the disk 3 is rotated under the condition that each magnetic head 2 is supported by the head supporting plates 1 in the manner described above so that the disk 3 is wound upward as shown in FIG. 3A, the magnetic head 2 follows the disk 3 so as to be displaced upward until downward bend, which has been previously in the head plate 1, is eliminated by the elastic recovery of the supporting plate 1.
However, after such bend of the head supporting plate 1 is eliminated, the magnetic head 2 cannot follow the surface of the disk 3. Thus, although the conventional head supporting plate 1 can follow the torsional displacement to some extent, the range in which the magnetic head 2 can follow the vertical winding of the disk 3 is very limited, because displacement in the vertical direction is very short.
Furthermore, when the disk 3 is forced to wind downward as shown in FIG. 3C, the bend of the head supporting plate 1 soon reaches its limit so that the pressure contact between the magnetic head 1 and the disk 3 becomes excessive, which may result in damages of the head 2 and the disk 3.